Transmitting acknowledgement messages using a staggered uplink time slot

ABSTRACT

A downlink communication is transmitted/received in at least one downlink time slot. In response to the received downlink communication, an acknowledgement message is received/transmitted in an uplink time slot a fixed integer number of uplink time slots after transmission/reception of the received downlink communication. The uplink and downlink time slots are staggered by substantially a half of a time slot.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/492,931 filed Sep. 22, 2014, which is a continuation of U.S. patentapplication Ser. No. 13/312,257 filed Dec. 6, 2011, which issued as U.S.Pat. No. 8,842,642 on Sep. 23, 2014, which is a continuation of U.S.patent application Ser. No. 12/246,190 filed Oct. 6, 2008, which issuedas U.S. Pat. No. 8,072,944 on Dec. 6, 2011, which is a continuation ofU.S. patent application Ser. No. 09/691,874 filed Oct. 19, 2000, whichissued as U.S. Pat. No. 7,433,340 on Oct. 7, 2008, which areincorporated by reference as if fully set forth.

BACKGROUND

In a wireless telecommunication system, radio channels provide aphysical link between communication units. The wireless communicationunits in such a system typically include a base station processor incommunication with a network such as the Public Switchboard TelephoneNetwork (PSTN), in the case of voice communication, or a data network,in the case of data communication, and one or more subscriber accessunits in communication with a plurality of end user computing devices,such as user PCs. The wireless channels include forward channels, formessage transmission from the base station processor to the subscriberaccess units, and reverse channels, for message transmission to the basestation processor from the subscriber access units.

In the case of a wireless data system such as may be used to providewireless Internet access, each base station processor typically servesmany subscriber access units, which in turn serve many end usercomputing devices. The wireless channels, however, are a scarceresource, and are therefore allocated by a scheduler among thesubscriber access units served by the base station processor. Thescheduler allocates the wireless channels among the subscriber accessunits on a traffic demand basis. One way of supporting on demand accessamong multiple users is so-called time division multiple access (TDMA)whereas each of the wireless channels are allocated to specificconnections only for a certain predetermined time intervals or timeslot. Message transmission is initiated at the beginning of each timeslot. A message queued for transmission via a wireless channel,therefore, remains queued until the beginning of the next time slot. Therate and duration of the time slots, therefore, define a messagetransmission cycle.

Often, a message transmission results in a return message beingtransmitted back to the sending wireless communication unit. Frequently,the return message is computed and queued for transmission in less thanthe predetermined interval defining the time slots. The return messagemay even be computed and enqueued in less than one half the duration ofa time slot. However, the return message must still wait enqueued untilthe next allocated time slot becomes available to the particularconnection. Therefore, transmission of the message and the returnmessage requires at least three time slots: one to transmit the message,a second during which the return message is computed, and a third totransmit the return message, even if the return message was computedwell before the second time slot completed.

Further, some channel allocation methods allocate a wireless channel forthe return message at the same time as allocating a channel for theinitial message which triggered the return message. The wireless channelallocated for the return message, therefore, remains allocated until thereturn message is received.

It would be beneficial, therefore, to provide a system and method forscheduling the time slots such that the forward cycle and the reversecycle are out of phase, therefore providing a time slot for a returnmessage in less than a full time slot interval.

SUMMARY OF THE INVENTION

An apparatus and method for staggering forward and reverse channel timeslot allocation in a wireless communication network allows a wirelesscommunication unit, such as a base station processor or a subscriberaccess unit, to transmit a return message in less than a full time slotinterval. Forward and reverse channel allocation occurs as a cycle oftime slots occurring at periodic timing intervals. Transmission of awireless frame carrying a message payload occurs at the beginning of thetime slot. Since the forward and reverse channel allocation cycles neednot be concurrent, or in phase, these cycles are staggered with respectto each other. By staggering the forward and reverse channel allocationtiming interval, the return message is sent after only a portion of afull timing interval, rather than being delayed up to one completetiming interval.

A set of forward channels and a set of reverse channels are designatedto transmit wireless messages between a subscriber access unit and abase station processor. The message transmission cycle for the forwardchannel and for the reverse channels do not need to be concurrent. Aforward cycle determines the time slots for the forward channel and areverse cycle determines the time slots for the reverse channel.

A message sent often results in a return message in the oppositedirection. A message sent via a forward channel may result in a returnmessage via a reverse channel Similarly, a message sent via a reversechannel may result in a return message being sent via a forward channel.Many return messages, however, do not require a full timing interval tocompute. By staggering, or offsetting, the forward and reverse channelallocation cycles, the time slots will be staggered, or overlap, ratherthan occurring in concurrent cycles. Return messages need to wait onlyfor the timing interval represented by the overlap. Therefore, returnmessages can be sent more quickly than if a full time slot duration wasto elapse. In this manner, a return message which requires only aportion of a timing interval to compute need only wait for a portion ofa full timing interval until a wireless channel is available to transmitthe return message.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 shows a block diagram of a wireless communication system suitablefor performing wireless channel allocation as defined herein;

FIG. 2 shows a prior art timing chart depicting transmission of amessage and a return message;

FIG. 3 shows a timing chart depiction transmission of a message and areturn message as defined herein;

FIG. 4 shows an example of message transmission via the wirelesscommunication system of FIG. 1;

FIG. 5 shows channel allocation and scheduling in greater detail; andFIG. 6 shows a timing diagram of scheduling a reverse channel.

DETAILED DESCRIPTION

FIG. 1 shows a wireless telecommunications system suitable forperforming staggered forward and reverse channel allocation. A pluralityof user PCs 12 a-12 e are each in communication with a subscriber accessunit (SAU) 14 a-d via a wired connection 20. The wired connectiontypically conforms to a wired protocol such as TCP/IP or UDP/IP.

The subscriber access units 14 a-14 d are in wireless communication witha base station processor (13SP) 16 via a wireless link 26. The wirelesslink 26 conforms to a wireless protocol such as IS 95 or anotherwireless protocol which supports communication via an RF medium. Thebase station processor 16 is also connected to a public access network18 such as the Internet, via an internetworking gateway 24. Theinternetworking gateway is typically a bridge, router, or otherconnection to a network backbone, and may be provided by a remoteprovider such as an Internet Services Provider (ISP). In this manner, anend user at the user PC 12 is provided a wireless connection to a publicaccess network 18 via the subscriber access unit 14 and the base stationprocessor 16.

Typically, a user PC 12 sends a message over a wired link 20, such as alocal area network or bus connection, to the subscriber access unit 14.The subscriber access unit sends a message via the wireless link 26 tothe base station processor 16. The base station processor 16 sends themessage to the public access network 28 via the internetworking gateway18 for delivery to a remote node 30 located on the network 28.Similarly, a remote node 30 located on the network can send a message tothe user PC by sending it to the base station processor 16 via theinternetworking gateway 24. The base station processor 16 sends themessage to the subscriber access unit serving the user PC 12 via thewireless link 26. The subscriber access unit sends the message to theuser PC 14 via the wired link 20. The subscriber access unit 14 and thebase station processor 16 can therefore be viewed as endpoints of thewireless link 26.

As indicated above, there are typically many more user PCs than thereare available wireless channel resources. For this reason, the wirelesschannels are allocated according to some type of demand-based multipleaccess technique to make maximum use of the available radio channels.Multiple access is often provided in the physical layer, such as byFrequency Division Multiple Access (FDMA) or by schemes that manipulatethe radio frequency signal such as Time Division Multiple Access (TDMA)or Code Division Multiple Access (CDMA). In any event, the nature of theradio spectrum is such that it is a medium that is expected to beshared. This is quite dissimilar to the traditional environment for datatransmission, in which a wired medium such as a telephone line ornetwork cabling is relatively inexpensive to obtain and to keep open allthe time.

In a typical wireless transmission, a message send often results in areturn message. A wireless channel is allocated to send the message, anda second wireless channel allocated in the opposite direction to sendthe return message. Wireless channel allocation can occur by a varietyof methods, such as that disclosed in U.S. patent application Ser. No.09/574,622, filed May 19, 2000, entitled “Automatic Reverse ChannelAssignment in a Two-Way TDM Communication System,” which issued intoU.S. Pat. No. 6,804,252 on Oct. 12, 2004, which is incorporated hereinby reference.

FIG. 2 illustrates a prior art message send and a return message send.Referring to FIGS. 2 and 3, time is shown along the horizontal axis 32.Wireless message transmission occurs at regular intervals as defined bythe channel allocation cycle. Each time slot in the channel allocationcycle is shown by increments 34 a-34 g. During the time slot beginningat 34 a, a message is sent from the base station processor 16 to thesubscriber access unit 14, shown by time block 36. During the next timeslot beginning at 34 b, the subscriber access unit 14 processes themessage and enqueues a return message, as shown by time block 38.Although the time to process and enqueue the return message requiredonly half of a full time slot interval, it remained enqueued until thebeginning of the next time slot since the wireless transmission occursat the beginning of each time slot. The return message is sent back tothe base station processor 16 during the time slot beginning at 34 c,and received by the base station processor at 34 d. A similar sequenceoccurs for the next message sent, as shown by time blocks 42, 44, and46. Each message sent has required three time slot intervals before thereturn message is received.

In a particular embodiment, the time slot intervals are approximately 26ms, due to the wireless protocol employed. These intervals are actually26.666 ms in duration, and are called an epoch. In this embodiment, asin the timing diagram of FIG. 3, the timeslot intervals are staggered byone-half, or approximately 13 ms. In another embodiment, the time slotscould be staggered by other amounts. Factors affecting the selection ofthe staggering amount include the volume of message traffic,availability of channels at the base station processor 16 and thesubscriber access units 14, and the likelihood of processing andenqueueing the return message before the beginning of the next timeslot. For example, if the return messages in one direction weretypically processed and enqueued in 16 ms and the return messages weretypically processed and enqueued in the opposite direction in 10 ms, itwould be beneficial to have the cycle corresponding to the 16 msprocessing time lead the opposite cycle by 10 ms. In this manner, a newtime slot would occur 16 ms. after the previous message was received.

FIG. 3 illustrates staggered channel allocation timing. Referring toFIGS. 1 and 3, the time slots of the forward channel allocation cycle isshown by the increments 48 a-48 f, while the time slots of the reversechannel allocation cycle is shown by increments 50 a-50 f. The time slotintervals of the forward and reverse channels are not in phase, butrather are staggered such that the time slot intervals for channels inone direction are offset one half time slot cycle out of phase with thetime slot intervals for channels in the opposite direction. During thetime slot beginning at 48 a, the base station processor 16 sends amessage to the subscriber access unit 14, shown by 52. About halfwaythrough the time slot from 48 a-48 b, a time slot 50 a begins on thesubscriber access unit 14, as defined by the reverse channel allocationcycle. As the base station processor 16 completes the messagetransmission at 48 b, the subscriber access unit is in the middle of atime slot. The return message, however, requires only one half of a timeslot interval to process and enqueue for transmission, as shown by timeblock 54.

As the time slot begun at 50 a expires at 50 b, the return message isenqueued for transmission. During the time slot from 50 b-50 c, thereturn message is sent from the subscriber access unit 14 to the basestation processor 16, shown by time block 56. A similar sequence occursat time blocks 58, 60, and 62. The return message is received by thebase station processor 16 only 2.5 time slot intervals after it wassent. Therefore, the wireless channel allocated for the return messageis available for other messages more quickly.

The system and method described herein is employed on both endpoints ofthe wireless link. Messages sent from the base station processor 16 tothe subscriber access unit 14, as well as messages sent from thesubscriber access unit 14 to the base station processor 16, are equallyapplicable to wireless channel allocation as described herein. Also, themessages described herein refer to sequences of data transmitted betweena subscriber access unit and a base station processor 16 during a timeslot interval. In a particular embodiment, these messages are link layermessages transmitted in accordance with the underlying wireless RFprotocol. The system and methods as claimed herein, however, could beapplied to other types of demand based scheduling of data transmission,such as message packets, frames, and fragments, at other layers oftransmission.

FIG. 4 shows an example of common a web page fetch via a browserapplication on a user PC using staggered channel allocation. Such a webpage fetch is typically in the form of packets containing data accordingto the Hypertext Markup Language (HTML). This type of transactiontypically results in many allocations of wireless channels and wirelessmessages as described above, as the data is manipulated according tovarious protocols prior to reaching the link level. Referring to FIG. 4.a user sends a web page fetch request from user PC 14 a. The message issent via the wired link 20 to the subscriber access unit 14 a as shownby arrow A. The subscriber access unit receives the message andprocesses it for transmission to the base station processor 16 as shownby arrow B. Transmission to the base station processor 16 occurs at C,via the wireless link 26, and includes a series of wireless messagescorresponding to the channel allocation described above with respect toFIG. 3. At D the wireless messages are reassembled, and sent to aninternetworking gateway 18 via wired link 24. The internetworkinggateway sends the HTML fetch to a remote node via the Internet 28, shownby arrow E. Arrow F denotes the requested HTML page returned from theremote node. The base station processor 16 receives the HTML page viathe wired link 24, and processes it for transmission to the subscriberaccess unit 14. As above, transmission to the subscriber access unitsoccurs via wireless messages over wireless channels allocated as aboveas described above with respect to FIG. 3, as shown by arrow H. Thesubscriber access unit reassembles the wireless messages into the HTMLpage, as shown by arrow I, and sends the HTML page to the user PC 12 a,as shown by arrow J.

The wireless channels described above typically transport messagesaccording to a wireless protocol, and contain wireless packed framinginformation. By way of example, the wireless packet framing informationmay be that described in Patent Cooperation Treaty Application No.W099/44341 entitled “Dynamic Frame Size Setting For MultichannelTransmission,” published Sep. 2, 1999, and which is hereby incorporatedby reference. In that scheme, Code Division Multiple Access (CDMA)encoding is used to define multiple logical channels on a given physicalchannel. For example, a long pseudo-random noise (PN) code sequence canbe used to define multiple logical channels on a given radio frequencycarrier signal. Other codes may be layered on the long PN code, such aserror correction codes or optional short pseudo-random noise (PN) codes,to further define the channels and make them robust in noisyenvironments.

In accordance with the link layer or even a higher layer TCP/IPprotocol, a receiving endpoint is expected to send an acknowledgmentmessage to the corresponding sending unit upon complete and correctreceipt of a packet. Referring to FIG. 5, this acknowledgment messagemay be sent in response in a cumulative fashion, such that a givenacknowledgment message indicates that a number of consecutive packetshave been received successfully. However, in any event, it can beappreciated that these acknowledgment messages in the system 10 must besent over the forward link 140 or reverse link 150 in response tomessages sent on the reverse 150 or forward 140 link, respectively.Given that the system 10 is a wireless system, radio resources musttherefore be provisioned for sending such acknowledgment messagesregardless of the exact physical layer configuration.

The channels comprising the forward and reverse links will now bediscussed in greater detail. In a particular embodiment, the reverselink 150 actually consists of a number of different types of logicaland/or physical radio channels including an access channel 151, multipletraffic channels 152-1, . . . 152-t, and a maintenance channel 153. Thereverse link access channel 151 is used by the subscriber access units14 to send messages to request that traffic channels be granted to them.The assigned traffic channels 152 then carry payload data from thesubscriber access unit 14 to the base station processor 16. It should beunderstood that a given IP level connection may actually have more thanone traffic channel 152 assigned to it as described in the previouslyreferenced patent application. In addition, a maintenance channel 153may carry information such as synchronization and power control messagesto further support transmission of information over the reverse link150.

Similarly, the forward link 140 typically includes a logical pagingchannel 141 that is used by the base station processor 16 to not onlyinform the subscriber access unit 14 that forward link traffic channels152 have been allocated to it, but also to inform the subscriber accessunit 14 of allocated traffic channels 152 in the reverse link direction.Traffic channels 142-1 . . . 142-t on the forward link 140 are used tocarry payload information from the base station processor 16 to thesubscriber access units 14. Additionally, maintenance channels carrysynchronization and power control information on the forward link 140from the base station processor 16 to the subscriber access units 14.

Additional information as to one possible way to implement the variouslogical channels 141, 142, 143, 151, 152, and 153 is also provided inPatent Cooperation Treaty Application No. W099/63682 entitled “FastAcquisition Of Traffic Channels For A Highly Variable Data Rate,”published Dec. 9, 1999.

As shown more particularly in FIG. 6, a typical forward link trafficchannel 142 is partitioned into a pre-determined number of periodicallyrepeating time slots 160-1, 160-2, . . . 160-n for transmission ofmessages to the multiple subscriber access units 14. A given subscriberaccess unit 14 identifies messages directed to itself based upon when amessage is received in an assigned time slot 160. It should beunderstood that a given subscriber access unit 14 may at any instant intime have multiple ones of the time slots 160 assigned to it or at othertimes may have no time slots assigned to it. The assignment of timeslots 160 is communicated from a central controller such as a wirelessInternet facility base station controller 23 or the base stationprocessor 16 itself over the paging channel 141. The allocation of radioand traffic channels occurs on a demand basis among the varioussubscriber access units 14 in a physical area serviced by the system 10.

The manner of assignment of the time slots and radio channels is not ofimportance to the present invention; rather the present invention ismore concerned with a particular embodiment in which a time slot 160 isscheduled in a staggered interval and assigned to the reverse link 150following reception of a valid message on the forward link 40.

In particular, the reverse link traffic channels 152 are shared amongthe multiple subscriber access units 14. For example, a given reverselink traffic channel 152-i is partitioned into a number of time slots170-1 . . . 170-n in a manner similar to the way in which the forwardlink traffic channel 142-i is partitioned.

Consider that a given forward link traffic channel 142-i may include aparticular time slot 160-4. This time slot 160-4 carries packet datafrom the base station processor 16 to an intended subscriber access unit14. However, unlike prior art systems, there is no specific assignmentneeded of reverse link traffic channel slots by sending paging channelmessages to inform the connection associated with the particular timeslot 160-4. Rather, upon receiving the data packet in time slot 160-4,the subscriber access unit 14 determines whether the data has beenproperly received such as by performing error check processing. If thepacket is indicated as having been received properly, the subscriberaccess unit 14 makes an assumption that the acknowledgment message willbe expected to be transmitted in corresponding time slot 170-4 on thereverse link traffic channel 152-i.

The time slot 170-4 is positioned timewise a given number of time slots,m, away from the time slot 160-4 allocated to the forward link. This, ineffect, results in automatic reservation of a reverse link time slot forthe acknowledgment message a fixed number of time slots, m, in thefuture.

Similarly, an acknowledgment message for a packet sent in time slot160-2 is acknowledged in the time slot 170-2. The time slot 170-2remains the m time slots away from its associated forward link time slot160-2.

Several advantages result from this arrangement. In particular, nocontrol signaling is required on the paging channel 141 to allocatereverse link time slots for the acknowledgment messages. The techniqueefficiently uses the reverse channel for acknowledgment messages such asTCP/IP layer ARQ messages among a large number of subscriber accessunits 14. The short time delay duration for these acknowledgmentmessages in turn increases the effective utilization of the trafficchannels 152 on the reverse link, as well as the paging channel 141 onthe forward link 140.

It should be understood that the time slot 170-4 can also carry othershort messages, such as link layer acknowledgment messages. In manyapplications, link layer acknowledgments must be handled rapidly, andthe invention provides this capability.

At higher protocol levels, the reverse time slot can be used for sendingembedded links in a Web page, as described above with respect to FIG. 4.For example, a typical Hypertext Transfer Protocol (HTTP) Web page filehas several embedded links which are requests to fetch other files.These embedded links can be sent back on the reverse channel using thetime slots 170-4.

Those skilled in the art should readily appreciate that the programsdefining the operations and methods defined herein are deliverable to asubscriber access unit and to a base station processor in many forms,including but not limited to a) information permanently stored onnon-writeable storage media such as ROM devices, b) informationalterably stored on writeable storage media such as floppy disks,magnetic tapes, CDs, RAM devices, and other magnetic and optical media,or c) information conveyed to a computer through communication media,for example using baseband signaling or broadband signaling techniques,as in an electronic network such as the Internet or telephone modemlines. The operations and methods may be implemented in a softwareexecutable out of a memory by a processor or as a set of instructionsembedded in a carrier wave. Alternatively, the operations and methodsmay be embodied in whole or in part using hardware components, such asApplication Specific Integrated Circuits (ASICs), state machines,controllers or other hardware components or devices, or a combination ofhardware, software, and firmware components.

While the system and method for staggered wireless channel allocationhave been particularly shown and described with references toembodiments thereof, it will be understood by those skilled in the artthat various changes in form and details may be made therein withoutdeparting from the scope of the invention encompassed by the appendedclaims. Accordingly, the present invention is not intended to be limitedexcept by the following claims.

What is claimed is:
 1. A code division multiple access (CDMA) wirelesssubscriber unit comprising a memory and at least one processor, thememory configured to store executable instructions, that when executedby the at least one processor, cause the CDMA wireless subscriber unitto: use a pseudo-random noise (PN) code combined with other codes todefine a plurality of channels on a given radio frequency carrier,wherein the plurality of channels includes at least a downlink channeland an uplink channel; receive a downlink communication in at least onedownlink time slot of the downlink channel; in response to the receiveddownlink communication, produce an acknowledgement message; and transmitthe acknowledgement message in an uplink time slot of the uplink channela fixed integer number of uplink time slots after reception of thereceived downlink communication; wherein the uplink time slot and thedownlink time slot are staggered by substantially a half of a time slot.2. The CDMA wireless subscriber unit of claim 1 wherein the downlinkcommunication includes TCP/IP data.
 3. The CDMA wireless subscriber unitof claim 1 wherein the acknowledgement is a link layer acknowledgement.4. The CDMA wireless subscriber unit of claim 1, wherein the uplink timeslot is not assigned to the subscriber unit by a network device.
 5. Amethod for use by a code division multiple access (CDMA) wirelesssubscriber unit comprising: using a pseudo-random noise (PN) codecombined with other codes to define a plurality of channels on a givenradio frequency carrier, wherein the plurality of channels includes atleast a downlink channel and an uplink channel; receiving a downlinkcommunication in at least one downlink time slot of the downlinkchannel; in response to the received downlink communication, producingan acknowledgement message; and transmitting the acknowledgement messagein an uplink time slot of the uplink channel a fixed integer number ofuplink time slots after reception of the received downlinkcommunication; wherein the uplink time slot and the downlink time slotare staggered by substantially a half of a time slot.
 6. The method ofclaim 5 wherein the downlink communication includes TCP/IP data.
 7. Themethod of claim 5 wherein the acknowledgement is a link layeracknowledgement.
 8. The method of claim 5, wherein the uplink time slotis not assigned to the CDMA wireless subscriber unit by a networkdevice.
 9. A code division multiple access (CDMA) network devicecomprising a memory and at least one processor, the memory configured tostore executable instructions, that when executed by the at least oneprocessor, cause the CDMA network device to: use a pseudo-random noise(PN) code combined with other codes to define a plurality of channels ona given radio frequency carrier, wherein the plurality of channelsincludes at least a downlink channel and an uplink channel; and transmita downlink communication in at least one downlink time slot of thedownlink channel; and in response to the transmitted downlinkcommunication, receive an acknowledgement message in an uplink time slotof the uplink channel a fixed integer number of uplink time slots aftertransmission of the transmitted downlink communication; wherein theuplink time slot and the downlink time slot are staggered bysubstantially a half of a time slot.
 10. The CDMA network device ofclaim 9 wherein the downlink communication includes TCP/IP data.
 11. TheCDMA network device of claim 9 wherein the acknowledgement is a linklayer acknowledgement.
 12. The CDMA network device of claim 9, whereinthe uplink time slot is not assigned by the CDMA network device.